Remove pbr version specifier
Remove pbr version specifier

Most of our dependencies now are relying on pbr>1.0, so the old
version specifier causes conflicts.

Change-Id: I16925a3b782ddaefeba3acf0ed315779cb34b119

dpkshetty/instack-undercloud,dmsimard/instack-undercloud,bcrochet/instack-undercloud,dmsimard/instack-undercloud,eprasad/instack-undercloud,dpkshetty/instack-undercloud,eprasad/instack-undercloud,bcrochet/instack-undercloud,rdo-management/instack-undercloud,rdo-management/instack-undercloud